The de Broglie wavelength, λ , of a 5-MeV alpha particle is 6.4 fm, as shown in this chapter, and the closest distance, rmin, to the gold nucleus this alpha particle can get is 45.5 fm (calculated in Example 39.1). Based on the fact that λ ≪ rmin, one can conclude that, for this Rutherford scattering experiment, it is adequate to treat the alpha particle as a